chem161sg_chapter8

chem161sg_chapter8 - Chapter 8 Electron Configurations...

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Chapter 8 Electron Configurations Atomic Properties and the Periodic Table Rigorous solution of Schrödinger’s equation is not possible for multi- electron systems. One has approximate solutions and the orbital energies depend on (n) and ( l ) . Electron configuration tells us how electrons are distributed among the various atomic orbitals. The energies of the subshells in a given shell is the same for the H-atom only . For multi-electron atoms, the various subshells [(s, p, d, …) orbitals] have different energies because of the e – e repulsions. Two factors determine the relative energies of these orbitals… 1. Penetration Effect An (s ) e is closer to the nucleus than a (p ) e . In other words, an (s ) electron penetrates more than a (p ) e in the same shell 2. Shielding Effect Because of the e – e repulsion, the full effect of the nucleus to attract these electrons is not completely realized. In other words, the effective nuclear charge is less than what it would be if the other electrons were not present. Since electrons in an (s ) orbital penetrate more, they are less shielded. Therefore, they are more tightly held . Thus, they are of lower energy than the (p ) electrons. In isolated multielectron atom, energy levels within a subshell are not split further. All three (p) orbitals are of the same energy and all the five (d) orbitals are of the same energy. Orbitals of the same energy are called degenerate orbitals. 1
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What is the order of the energy levels? 1s < 2s < 2p < 3s < 3p < 4s < 3d NOTE: the 4s orbital may have a lower energy than the 3d orbital because of its penetrating power. Aufbau Principle: This states that in writing the electron configuration in multi-electron atoms, one starts filing the lower energy orbitals first,then goes to the higher energy orbitals. Pauli’s Exclusion Principle: A maximum of two electrons may occupy a given orbital and no two electrons in an orbital can have the same four quantum numbers. He has 2 e electron configuration 1s 2 (shell number 1) ruled out when two electrons reside in the same orbital, their spins must be paired. n = 1 l = 0 m l = 0 m s = +1/2 n = 1 l = 0 m l = 0 m s = –1/2 Hund’s Rule: The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins. not… nor… C: has six electrons. Electron configuration… C : 1 s 2 2s 2 2p 2 N: has seven electrons. Electron configuration… These violate Hund’s rule!!! N : 1 s 2 2s 2 2p 3 O: has eight electrons. Electron configuration… O: 1s 2 2s 2 2p 4 2
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Energy Level Diagram 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 5g Follow the Arrow: this gives the relative energies of the various orbitals. Start filling from the lower E and going up to the higher E. “n +
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chem161sg_chapter8 - Chapter 8 Electron Configurations...

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